Projected Impacts of Climate and Land-Use Change on the Global Diversity of Birds

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Abstract
Over the past few decades, land-use and climate change have led to substantial range contractions and species extinctions. Even more dramatic changes to global land cover are projected for this century. We used the Millennium Ecosystem Assessment scenarios to evaluate the exposure of all 8,750 land bird species to projected land-cover changes due to climate and land-use change. For this first baseline assessment, we assumed stationary geographic ranges that may overestimate actual losses in geographic range. Even under environmentally benign scenarios, at least 400 species are projected to suffer >50% range reductions by the year 2050 (over 900 by the year 2100). Although expected climate change effects at high latitudes are significant, species most at risk are predominantly narrow-ranged and endemic to the tropics, where projected range contractions are driven by anthropogenic land conversions. Most of these species are currently not recognized as imperiled. The causes, magnitude and geographic patterns of potential range loss vary across socioeconomic scenarios, but all scenarios (even the most environmentally benign ones) result in large declines of many species. Whereas climate change will severely affect biodiversity, in the near future, land-use change in tropical countries may lead to yet greater species loss. A vastly expanded reserve network in the tropics, coupled with more ambitious goals to reduce climate change, will be needed to minimize global extinctions. Land conversion and climate change have already had significant impacts on biodiversity and associated ecosystem services. Using future land-cover projections from the recently completed Millennium Ecosystem Assessment, we found that 950–1,800 of the world's 8,750 species of land birds could be imperiled by climate change and land conversion by the year 2100. These projections are based on the assumption that birds will not dramatically shift their ranges in response to a changing climate, a process that would lessen the range contractions we predict. While climate change will be the principal driver of range contractions at higher latitudes, our projections reveal that land conversion (e.g., deforestation, conversion of grasslands to croplands, etc.) will have a much larger effect on species that inhabit the tropics. This is because birds in the tropics are especially diverse and tend to have small ranges, making them particularly vulnerable to extinction; in contrast, birds at higher latitudes are less diverse and tend to have large ranges. A vastly expanded reserve network in the tropics, coupled with more ambitious goals to reduce greenhouse gas emissions and monitor biodiversity impacts, will be needed to minimize global extinctions.